EPDM—陶瓷高介电常数低损耗复合电介质薄膜

采用三元乙丙橡胶（ＥＰＤＭ） 与高介电常数陶瓷粉复合制备高介电常数低损耗复合电介质薄膜,解决聚丙烯—陶瓷复合电介质膜发脆问题。对ＥＰＤＭ 和不同陶瓷粉体的复合进行了较系统的研究,对影响复合电介质薄膜性能的因素、复合工艺条件等作了探讨。在保持复合薄膜柔软的条件下,介电常数达３０,比ＥＰＤＭ 大幅度提高且损耗很小,容量温度变化率小于５％ （－２５℃～８５℃）。体积电阻率１０１５Ωｃｍ ,击穿强度大于５０ｋＶ／ｍｍ 。     

Fine-tuning of negative permittivity behavior in amorphous carbon/alumina metacomposites

In this work, amorphous carbon/alumina (C/Al₂O₃) metacomposites with tunable negative permittivity were synthesized by a facile impregnation method. We analyzed the influence of carbon content and the carbonization temperature on the microstructure and electrical properties of the metacomposites. It was found that the conductive carbon networks were formed in the composites with the higher carbon contents and carbonization temperatures, which lead to the appearance of a metal-like conduction and negative permittivity behavior. Low-frequency plasmonic state provided by plenty of free electrons in the carbon networks resulted in the negative permittivity, and its numerical values could be effectively adjusted by controlling the carbon content and carbonization temperature, which could be well explained by Drude model. This work provides a feasible way to prepare metacomposites with tunable negative permittivity, which will expand their potential applications in shielding, absorbing and novel capacitor fields.     

A new perovskite-related ceramic with colossal permittivity and low dielectric loss

We designed a new type of perovskite-related dielectric energy storage material Na_1/3Cd_1/3Bi_1/3Cu₃Ti₄O₁₂ with colossal permittivity via an ordinary solid-state method. Remarkably, the Na_1/3Cd_1/3Bi_1/3Cu₃Ti₄O₁₂ ceramic sintered at 1030 °C displays a decent dielectric performance of colossal permittivity ∼1.5 × 10⁴ and low dielectric loss ∼0.04 at 1 kHz. Electric heterogeneity structure in Na_1/3Cd_1/3Bi_1/3Cu₃Ti₄O₁₂ ceramics was clarified, which consists of insulating grain boundaries and semiconducting grains. Notably, internal barrier layer capacitor effect was adopted to explain the decent dielectric performance based on the analysis of dielectric response behavior and complex impedance. Three dielectric anomalies were evidenced in dielectric temperature spectra. Our finding in this work not only explored the dielectric response of the new type of giant dielectric ceramics Na_1/3Cd_1/3Bi_1/3Cu₃Ti₄O₁₂ but also provided candidate materials for high energy storage density capacitors.     

Low-frequency plasmonic state and tunable negative permittivity in percolative graphite / barium titanate composites

Percolative composites with negative permittivity have attracted widespread attentions due to their great potential in electromagnetic shielding and microwave devices. Targeting at achieving epsilon-negative properties, the percolative graphite/barium titanate (GR/BaTiO₃) composite is herein designed and prepared using hot-pressing sintered process. It's found that the plasma oscillations of delocalized electrons result in the epsilon negative permittivity behaviors when the GR contents exceeds the 2 wt% (percolation threshold), and frequency dependence of the negative permittivity which is in well agreement with the Drude model. Meanwhile, it's demonstrated that the ac conductivity represents a typical metal-like behavior as the conductive networks formed within the composites by the increasing GR loadings. Moreover, the equivalent circuit analysis reveals the relationships between capacitive-inductive transition and the conversion of permittivity changing from positive to negative. This work provides effective possibility for developing excellent dielectric properties of percolative GR/BaTiO₃ composite for capacitors and coil-less electrical inductors applications.     

Dielectric properties with high dielectric permittivity and low loss tangent and nonlinear electrical response of sol-gel synthesized Na1/2Sm1/2Cu3Ti4O12 perovskite ceramic

Giant dielectric ceramic, Na_1/2Sm_1/2Cu₃Ti₄O₁₂, was successfully prepared by a modified sol-gel method. X-ray diffraction experiments indicated that a body-centered cubic structure with a space group of Im3 was obtained. Our density functional theory calculations revealed that codoping Na and Sm in the CaCu₃Ti₄O₁₂ structure resulted in charge compensation between Na and Sm ions in this structure, whereas the oxidation states of Cu and Ti were unaltered. Giant dielectric permittivity ～7.21 × 10³ - 8.04 × 10³ and low dielectric loss tangent ～0.045–0.049 were accomplished at a sintering temperature of 1050 °C for 12–18 h. Nonlinear J - E property with breakdown electric field ～5.13 – 5.78 × 10³ V/cm and nonlinear coefficient ～6.08–6.82 were also achieved. The n-type semiconducting grain originated from short-range migrations of mixed Cu⁺/Cu²⁺ and Ti³⁺/Ti⁴⁺ charges. Finally, our charge analysis showed that the occurrence of Cu⁺ and Ti³⁺ was related to the existence of oxygen vacancy in these ceramics.     

In-situ synthesis and characterization of electrically conductive polypyrrole/graphene nanocomposites

Polypyrrole (PPy)/graphene (GR) nanocomposites were successfully prepared via in-situ polymerization of graphite oxide (GO) and pyrrole monomer followed by chemical reduction using hydrazine monohydrate. The large surface area and high aspect ratio of the in-situ generated graphene played an important role in justifying the noticeable improvements in electrical conductivity of the prepared composites via chemical reduction. X-ray photoelectron spectroscopy (XPS) analysis revealed the removal of oxygen functionality from the GO surface after reduction and the bonding structure of the reduced composites were further determined from FTIR and Raman spectroscopic analysis. For PPy/GR composite, intensity ratio between D band and G band was high (∼1.17), indicating an increased number of c-sp² domains that were formed during the reduction process. A reasonable improvement in thermal stability of the reduced composite was also observed. Transmission electron microscopy (TEM) observations indicated the dispersion of the graphene nanosheets within the PPy matrix.     

Calcium copper titanate/polyurethane composite films with high dielectric constant,low dielectric loss and super flexibility

Calcium copper titanate(CCTO)/polyurethane composite films with high dielectric constant, low dielectric loss and super flexibility were fabricated by incorporating CCTO ceramic powders into millable polyurethane elastomer (MPU) matrix using a rubber milling combined with hot compression molding method. The composite films show uniform microstructures and the dielectric constant is as high as 35.2 while the dielectric loss is only 0.041 when CCTO content reaches 40 vol% at 100 Hz and room temperature (RT). Moreover, it is important to note that this film has stable dielectric constant and dielectric loss in a relatively wide temperature range (from 0 °C to 70 °C), which is significantly import to the practice use of electronic devices based on CCTO composites. In addition, the flexibility of the film could be retained even when the CCTO content is up to 40 vol% and the elongation at break of this composite film is as high as 159.1%. Theoretical analysis indicates that the experimental data are in good conformity to the effective medium theory (EMT) model with a derived n = 0.21, suggesting more close association of the dielectric constant with the CCTO filler size and shape.     

Giant permittivity and low dielectric loss of Fe doped BaTiO3 ceramics: Experimental and first-principles calculations

Fe doped BaTiO₃ ceramics with giant permittivity and low dielectric loss were synthesized in N₂/H₂ atmosphere started with BaTiO₃ powders and iron powders. XRD analysis exhibited the tetragonal-pseudocubic phase transition when the Fe content is 3 mol%. XPS spectra confirmed the iron oxides with mixed-valence structure of Fe²⁺/Fe³⁺, while Ti-ions maintain Ti⁴⁺3d⁰ states without any oxidization-reduction. For the case of ceramics with 5 mol% Fe, the dielectric constant was 66,650 at 1000 Hz at room temperature, 19 times higher than that of pure BaTiO₃ ceramics, while the dielectric loss tangent was 0.13. Comparison with other giant-permittivity materials demonstrated the superior potential of present ceramics. First-principles calculations investigated the interfacial interaction of Fe-[TiO₂] interface and Fe-[BaO] interface. Giant dielectric constant was induced by the interfacial polarization between insulating ferroelectrics and semiconducting iron oxides with mixed-valence states, as well as the contribution from the generated electron hopping conduction.     

Giant permittivity and low dielectric loss of SrTiO3 ceramics sintered in nitrogen atmosphere

The dielectric properties of SrTiO₃ ceramics sintered in nitrogen (N₂) exhibit a weak temperature- and frequency-dependent giant permittivity (>10⁴) as well as a very low dielectric loss (mostly < 0.02) over a broad temperature range from −100 to 200 °C. Based on the results of ac conductivity and structural analysis, the giant permittivity and low dielectric loss were due to the fully ionized oxygen vacancies and giant defect-dipoles. When further sintering these ceramics in air, the materials exhibit a large temperature- and frequency-dependent high dielectric loss, which were due to the ionization and motion of oxygen vacancies.     

Low-loss and temperature-stable negative permittivity in La0.5Sr0.5MnO3 ceramics

Materials with negative permittivity need to be used at different temperatures, while the negative permittivity behavior affected by large fluctuations in temperature has seldom been studied. In this work, La_0.5Sr_0.5MnO₃ ceramics were prepared by a sol-gel auto-combustion method and subsequent sintering. The negative permittivity behavior, electrical conductivity and reactance of La_0.5Sr_0.5MnO₃ ceramics were systematically studied at various temperatures. The fluctuation in negative permittivity is less than 2.6 % and the dielectric loss (tanδ) is less than 0.2 in the temperature range of 50–600 °C. Based on the key governing properties being achieved, the present work experimentally demonstrates that La_0.5Sr_0.5MnO₃ ceramics, as single-phase oxides, can be used as a feasible alternative metamaterial in a wide temperature range.     

Synthesis of CaAl2xB2O4+3x: Novel microwave dielectric ceramics with low permittivity and low loss

Novel CaAl_2xB₂O_4+3x (x = 0.25, 0.5, 0.75, and 1) ceramics were prepared via solid-state reaction method. The investigation is concentrated on sintering behavior, phase composition and dielectric properties of CaAl_2xB₂O_4+3x ceramics with various ratios of Al₂O₃ content. The optimal sintering temperature and the content of CaAl₂B₂O₇ are highly related to the variation of x value. CaAl_2xB₂O_4+3x ceramics possess excellent microwave dielectric properties: ε_r = 5.8 ± 0.05, Q × f = 63,338 ± 2690 GHz (@13.57 GHz), and τ_f=-29 ± 2 ppm/℃ when sintered at 940 ℃ for x = 0.5. Comparing the properties of CaAl_2xB₂O_4+3x ceramics with reported borate ceramics, the ceramics prepared in this study with low dielectric loss and low sintering temperature have promising prospects in LTCC technology.     

Low temperature preparation of CaCu3Ti4O12 ceramics with high permittivity and low dielectric loss

Low temperature preparation of CaCu₃Ti₄O₁₂ ceramics with large permittivity is of practical interest for cofired multilayer ceramic capacitors. Although CaCu₃Ti₄O₁₂ ceramics have been prepared at low temperatures as previously reported, they have rather low permittivity. This work demonstrates that CaCu₃Ti₄O₁₂ ceramics can not only be prepared at low temperatures, but they also have large permittivity. Herein, CaCu₃Ti₄O₁₂ ceramics were prepared by the solid state reaction method using B₂O₃ as the doping substance. It has been shown that B₂O₃ dopant can considerably lower the calcination and sintering temperatures to 870 °C and 920 °C, respectively. The relative permittivity of the low temperature prepared CaCu₃Ti_4−xB_xO₁₂ ceramics is about 5 times larger than the previously reported results in the literature. Furthermore, the dielectric loss of the CaCu₃Ti_4−xB_xO₁₂ ceramics is found to be as low as 0.03. This work provides a beneficial base for the future commercial applications of CaCu₃Ti₄O₁₂ ceramics with large permittivity for the cofired multilayer ceramic capacitors.     

Graphene platelets/aluminium nitride metacomposites with double percolation property of thermal and electrical conductivity

Graphene platelets/aluminium nitride (GPLs/AlN) metacomposites with double percolation property of thermal and electrical conductivity were successfully fabricated by spark plasma sintering. Microstructures and phase composition of the GPLs/AlN metacomposites were investigated by field emission scanning electron microscopy, X-ray diffraction and Raman spectroscopy. With increase of the GPLs contents, the double percolation property of thermal (19.27?wt% GPL) and electrical conductivity (19.03?wt% GPL) was found. Moreover, the negative permittivity behavior was also observed when the GPLs content reached 19.50?wt%, which was attributed to the formation of continuous GPLs networks. Finally, the equivalent circuit models were used to analyze the negative permittivity behavior. As the reactance (Z′′) converted from negative to positive, the inductors were introduced into the equivalent circuit models, and the GPLs/AlN metacomposites went through the capacitive-inductive transition with the increasing GPLs content, corresponding to the negative permittivity behavior.     

High-k composites with sandwich structure by introducing a negative permittivity layer with Ni as conductive filler

Advanced electronic equipment requires new high dielectric constant materials. Nevertheless, the balance of the permittivity and dielectric loss remained a problem. In this work, BFT/PVDF-Ni/PVDF sandwich polymer matrix composites (SPMCs) containing alternating negative dielectric constant and positive dielectric constant layers were fabricated using hot press sintering. The structure and dielectric properties of the composites were investigated. The results indicated that introducing negative dielectric constant layer into SPMCs led to higher dielectric constant (ε′ ≈ 130) and low loss tangent (tanδ ≈ 0.14) at 1 kHz compared with the pristine PVDF (ε′ ≈ 10, tanδ ≈ 0.020). The effective increase of dielectric constant was due primarily to the introduction of a negative dielectric layer into the material. The low loss tangent was caused by the ohm barrier effect between adjacent layers.     

Freeze-drying assisted fabrication of highly homogenized reduced graphene oxide/alumina metacomposites with negative permittivity

Graphene oxide (GO) was used to fabricated the highly homogenization reduced graphene oxide (RGO)/alumina (Al₂O₃) metacomposites with low percolation threshold and adjustable negative permittivity by spark plasma sintering method. Compared to the dry grinding method used for the graphene(GR)/Al₂O₃ and GR/AlN metacomposites reported in our previous work, the highly homogenization RGO/Al₂O₃ metacomposites were obtained based on freeze-drying. The microstructures and phase composition of the RGO/Al₂O₃ metacomposites were investigated by field emission scanning electron microscopy, X-ray diffraction and Raman spectroscopy. The dielectric properties including permittivity (ε′ and ε′′), dielectric loss tangent (tan?δ), alternating current conductivity (σ_ac) and reactance (Z′′) were discussed in detail. The percolation phenomenon of σ_ac was observed when the content of RGO increased from 13.50 to 15.38?wt%, and the percolation threshold fitted by the power law was 14.31?wt%, which appeared earlier than the reported GR/Al₂O₃ and GR/AlN metacomposites. What's more, the negative permittivity behavior was observed when the content of RGO reached 13.50?wt%, which was ascribed to the formation of continuous three-dimensional RGO network among the metacomposites. The RGO_13.50/Al₂O₃ and RGO_15.38/Al₂O₃ metacomposites realized the ε′ transition from negative to positive at 501 and 299?MHz, corresponding to the capacitive-inductive conversion.     

Low-frequency plasmonic state and negative permittivity in copper/titanium dioxide percolating composites

The titanium dioxide-based varistor is generally equivalent to a combination of resistor and capacitor, whereas, for the titanium dioxide-based composite with negative permittivity, it can be composed of a resistor, capacitor, and inductor. In this work, ac conductivity, real permittivity, and reactance of copper/titanium dioxide (Cu/TiO₂) percolating composites are investigated in detail in the frequency of 10 kHz - 1 MHz. As Cu content increases, percolation occurs in composites, accompanied by the transformation of electron transport mechanism from localization to delocalization. Furthermore, the regulation of permittivity by compositions and microstructures is specifically analyzed. It suggests that the enhanced permittivity before percolation ascribes to the enhancement of interfacial polarization, when reaching the excessively percolating state, plasma-like negative permittivity is achieved, consequently, revealing the low-frequency plasmonic state. Moreover, reactance analyses indicate the negative permittivity is ascribed to the inductive characteristics, and the stronger the inductance, the greater the contribution to the negative permittivity.     

Controlling negative permittivity and permeability behavior in LaFeO3 through sintering temperature

In this paper, the resonance behavior of LaFeO₃ in the GHz range was investigated. Synthesis of LaFeO₃, by solid state reaction between Fe₂O₃ and La₂O₃, was confirmed by X-ray diffractometry. LaFeO₃ exhibited dielectric resonance and magnetic resonance, which can lead to negative permittivity and negative magnetic permeability. By controlling sample synthesis parameters, specifically sintering temperature, the peak in negative permeability can be tuned between 2.6 and 2.8 GHz, while the peak in negative permittivity can be tuned between 0.8 and 1.2 GHz. This material can be applied to fields such as electromagnetic metamaterials, where it could be used to increase the gain of an antenna, or to control the transmission of microwaves.     

Core‐shell structured Al/PVDF nanocomposites with high dielectric permittivity but low loss and enhanced thermal conductivity

Surface modification of core‐shell structured Al (Al@Al₂O₃) nanoparticles was performed using γ‐(Aminopropyl)‐triethoxysilane (APS) and dopamine (DA), respectively, and the microstructures, dielectric properties and thermal conductivities of the Al/poly(vinylidene fluoride) (PVDF) nanocomposites were investigated. Both DA and APS enhance the interfacial bonding strength between the fillers and the matrix, leading to homogeneous dispersion of Al nanoparticles in PVDF matrix. Compared with raw Al nanoparticles, surface‐treated Al/PVDF exhibit much higher dielectric permittivity due to the enhanced interfacial interactions between the two components, whereas, the dielectric loss and electric conductivity of the nanocomposites still remain at rather low levels owing to the insulating alumina shell preventing effectively core Al from direct contact. The dynamic dielectric properties results reveal that dielectric constant and loss increase with temperature due to the gradually enhanced mobility of molecular chain segments of PVDF for the raw Al/PVDF and treated Al/PVDF nanocomposites. Additionally, the PVDF nanocomposites with Al treated with APS and DA show enhanced thermal conductivities compared with raw Al/PVDF under the same filler loading because of reduced thermal interfacial resistance promoting phonon transfer across the interfaces. POLYM. ENG. SCI., 59:103–111, 2019. © 2018 Society of Plastics Engineers     

Silicone elastomers with high dielectric permittivity and high dielectric breakdown strength based on dipolar copolymers

Dielectric elastomers (DEs) are a promising new transducer technology, but high driving voltages limit their current commercial potential. One method used to lower driving voltage is to increase dielectric permittivity of the elastomer. A novel silicone elastomer system with high dielectric permittivity was prepared through the synthesis of siloxane copolymers, thereby allowing for the attachment of high dielectric permittivity molecules through copper-catalysed azide-alkyne 1,3-dipolar cycloaddition (CuAAC). The copolymers have a high degree of chemical freedom, as the dimethylsiloxane spacer units between the functional groups, as well as the degree of functionalisation, can be varied. Thus, the best overall properties were obtained for an elastomer prepared with a copolymer with a 1200 g mol⁻¹ dimethylsiloxane spacer unit and 5.6 wt% of the high dielectric permittivity molecule 1-ethynyl-4-nitrobenzene. Here, a high increase in dielectric permittivity (∼70%) was obtained without compromising other favourable DE properties such as elastic modulus, gel fraction, dielectric loss and electrical breakdown strength.